Bendtsen et al. Environmental Health (2021) 20:10 https://doi.org/10.1186/s12940-020-00690-y REVIEW Open Access A review of health effects associated with exposure to jet engine emissions in and around airports Katja M. Bendtsen1* , Elizabeth Bengtsen1, Anne T. Saber1 and Ulla Vogel1,2 Abstract Background: Airport personnel are at risk of occupational exposure to jet engine emissions, which similarly to diesel exhaust emissions include volatile organic compounds and particulate matter consisting of an inorganic carbon core with associated polycyclic aromatic hydrocarbons, and metals. Diesel exhaust is classified as carcinogenic and the particulate fraction has in itself been linked to several adverse health effects including cancer. Method: In this review, we summarize the available scientific literature covering human health effects of exposure to airport emissions, both in occupational settings and for residents living close to airports. We also report the findings from the limited scientific mechanistic studies of jet engine emissions in animal and cell models. Results: Jet engine emissions contain large amounts of nano-sized particles, which are particularly prone to reach the lower airways upon inhalation. Size of particles and emission levels depend on type of aircraft, engine conditions, and fuel type, as well as on operation modes. Exposure to jet engine emissions is reported to be associated with biomarkers of exposure as well as biomarkers of effect among airport personnel, especially in ground-support functions. Proximity to running jet engines or to the airport as such for residential areas is associated with increased exposure and with increased risk of disease, increased hospital admissions and self- reported lung symptoms. Conclusion: We conclude that though the literature is scarce and with low consistency in methods and measured biomarkers, there is evidence that jet engine emissions have physicochemical properties similar to diesel exhaust particles, and that exposure to jet engine emissions is associated with similar adverse health effects as exposure to diesel exhaust particles and other traffic emissions. Keywords: Jet engine emissions, Airports, Occupational exposure, Particulate matter, Polycyclic aromatic hydrocarbons, Biomarkers * Correspondence: [email protected] 1National Research Centre for the Working Environment, Lersø Parkallé 105, DK-2100 Copenhagen, Denmark Full list of author information is available at the end of the article © The Author(s). 2021, corrected publication February 2021. 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The Creative Commons Public Domain Dedication waiver (http:// creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated in a credit line to the data. Bendtsen et al. Environmental Health (2021) 20:10 Page 2 of 21 Background key papers and systematic searches (search terms, method Exposure to air pollution, including ultrafine particulate and selection criteria are disclosed in the Additional file 1). matter (UFP), from industry and traffic is associated with We briefly summarize the characteristics of jet engine emis- adverse health effects [1–4]. Airports are significant high- sions and highlight the complexity of this field of research, emission sources and human exposure to these emissions but detailed research on emissions and physical-chemical is a growing health concern. Importantly, airport personnel studies is beyond the scope of this review. are at risk of occupational exposure to jet engine emissions [5]. More knowledge is needed on exposure risks, adverse Toxicity of jet fuel exposure health effects, biomarkers and risk management options re- The toxicity of (unburned) jet fuel as such has been con- lated to the diverse factors influencing human exposure to sidered in many studies (reviewed in [10]) since the early airport emissions [6](Fig.1). 1950’s, where the specifications of the hydrocarbon- However, data collection seems challenging. Commer- based jet fuel, JP-4 (jet propellent-4), was published by cial airports are large, complex and diverse work places, the US air force. Major toxic effects reported for JP-4 where aircraft, ground-support equipment (GSE), and re- were skin irritation, neurotoxicity, nephrotoxicity, and lated vehicles all contribute to mixed emissions [7, 8]. In renal carcinogenicity in rats [11]. Jet fuels are mixtures turn, commercial airports as well as military air stations of gasoline and kerosene with performance additives are year-round active high security areas with restricted [10]. In 1994, US Air Force converted to JP-8, developed access, which can reduce the options for external re- to be less volatile and less explosive upon crash incidents searchers to collect optimal or sufficient measurements. compared to JP-4. JP-8 (NATO F-34) is equivalent to Jet Consensus or formal guidelines for optimal measurement A-1 fuel used in commercial aircraft. A range of other design, instrumentation and analysis methods for the dif- kerosene-based jet fuels are in use, depending on aircraft ferent emission components are lacking, which further type and differing in kerosene ratio and requirements complicates comparison of data and risk assessment [5, 9]. for additives [5]. Measurements of a range of the com- With this review, we seek to compile available studies in mon aircraft pollutants such as benzene, toluene, and the open scientific literature on health effects of jet engine chlorinated compounds in breath samples from exposed emissions in occupational settings and in residential areas personnel on an airbase before and after work tasks around airports, along with mechanistic effects studied in showed significant exposure for all subjects, ranging animal and cell models. The studies were selected based on from minor elevations up to > 100 times the values of Fig. 1 Overview of contributing factors in exposure risks from airports (APU: auxiliary power unit; GAC: ground air-conditioning cart, ECS: environmental control system). Bendtsen et al. Environmental Health (2021) 20:10 Page 3 of 21 the control group for fuel workers [12]. The uptake of concentrations across exposure studies at airports, but JP-8 components both occur via inhalation and dermal data is limited as noted by Stacey [9]. contact, and apart from benzene, naphthalene in air and In general, emission levels are high, but vary depend- in exhaled breath condensate (EBC) may be useful as a ing on engine conditions and fuel type, as well as on op- biomarker of exposure to and uptake of JP-8 fuel com- eration modes such as idling, taxi, take-off, climb-out ponents in the body [13]. Although most studies report and landing [29]. low acute toxicity for both JP-4 and JP-8, JP-8 was re- ported to show effects such as respiratory tract sensory Particulate matter (PM) irritation [11], inflammatory cytokine secretion in ex- PM is divided by size ranges according to the aero- posed alveolar type II epithelial cells and in pulmonary dynamic diameter of the particles, where UFP are in the alveolar macrophages [14], increased pulmonary resist- nanoscale of < 100 nm. Several studies have shown that ance and decreased weight gain in rats upon inhalation aircraft emissions are dominated or even characterized exposure for 7 or 28 days [15, 16]. Subchronic 90-days by high concentrations of very small particles. This was studies with rats with various exposure levels of JP-4 and underlined in a recent study by Stacey, Harrison and JP-8 showed little toxicity, apart from male rat hydrocar- Pope carried out at Heathrow London in comparison to bon nephropathy [11]. However, JP-8 fuel exposure has traffic background [30]. Some report particles in the been linked to noise-activated ototoxic hearing loss in range of 5–40 nm [31], and others particle diameters of animal studies [17, 18] and in occupational exposure 20 nm as compared to larger particles of > 35 nm mea- cases [19, 20], and to immunotoxicity [21, 22]. sured at surrounding freeways [32]. Campagna et al. It is likely that fuel refinements will advance in the fu- studied the contributions of UFP from a military airport ture and be an important factor in emission reductions. to the surrounding area, by sampling on the airport A newer synthetic jet fuel (Fischer-Tropsch Synthetic grounds during flight activities, nearby the airport, in an Paraffinic Kerosene) under development to replace JP-8 urban area and in a rural area. The smallest primary par- in the future, was evaluated for toxicity in the required ticles were found within the airport (~ 10 nm) and the range of tests used to develop occupational exposure largest in the urban area (~ 72 nm). The highest UFP limits (OELs). The highest exposure level of 2000 mg/m3 levels inside the airport were measured during taxi and (6 h per day, 5 days a week for 90 days) produced multi- take-off activities (4.0 × 106 particles/cm3)[33]. Wester- focal inflammatory cell infiltrations in rat lungs, whereas dahl et al. reported very high particle number concentra- no genotoxicity or acute inhalation effects were ob- tions at take-off of a single jet aircraft, with a 10 s peak 3 served, and the sensory irritation assay indicated that the of 4.8 million particles/cm together with elevated NOx refined synthetic fuel was less irritating than JP-8 [23].